Defect Absorption in Ge 2 Sb 2 Te 5 Phase‐Change Films

Defect absorption spectra in amorphous and crystalline Ge 2 Sb 2 Te 5 phase‐change films are investigated. Photothermal deflection spectroscopy extended to the IR region reveals subgap absorption of the Ge 2 Sb 2 Te 5 films. Subgap absorption peaks are observed around 0.480, 0.415, and 0.368 eV for as‐deposited films, around 0.475, 0.410, and 0.360 eV for 180 °C‐annealed films, and around 0.410 and 0.350 eV for 300 °C‐annealed films at room temperature. The intensity and energies of the absorption peaks vary with heat treatments in the range of 90–300 °C. Broad absorption of 0.5–0.6 eV is also observed for as‐deposited films. Based on the experimental results, the generation mechanisms of the defect levels in amorphous, metastable, and stable crystalline Ge 2 Sb 2 Te 5 are discussed.